The field of the present disclosure relates to methods for producing silane and, particularly, methods which include use of electrolysis to regenerate reactive components. Some particular embodiments are directed to methods in which the production of silane is substantially “closed-loop” with respect to halogen and/or to an alkali or alkaline earth metal.
Silane is a versatile compound that has many industrial uses. In the semiconductor industry, silane may be utilized for deposition of an epitaxial silicon layer on semiconductor wafers and for production of polycrystalline silicon. Polycrystalline silicon is a vital raw material used to produce many commercial products including, for example, integrated circuits and photovoltaic (i.e., solar) cells that may be produced by thermal decomposition of silane onto silicon particles in a fluidized bed reactor.
Silane may be produced by reacting silicon tetrafluoride with an alkali or alkaline earth metal aluminum hydride such as sodium aluminum tetrahydride as disclosed in U.S. Pat. No. 4,632,816 which is incorporated herein by reference for all relevant and consistent purposes. This process is characterized by high energy efficiency; however, starting material costs can negatively influence the economics of such a system.
Silane may alternatively be produced by the so-called “Union Carbide Process” in which metallurgical-grade silicon is reacted with hydrogen and silicon tetrachloride to produce trichlorosilane as described by Müller et al. in “Development and Economic Evaluation of a Reactive Distillation Process for Silane Production,” Distillation and Adsorption: Integrated Processes, 2002, which is incorporated herein for all relevant and consistent purposes. The trichlorosilane is subsequently taken through a series of disproportionation and distillation steps to produce a silane end-product. This process requires a number of large recycle streams which increases the initial equipment costs as well as operating costs.
A continuing need therefore exists for economical methods for producing silane and for methods that are closed-loop with respect to certain materials used within the production process. A need also exists for systems for performing such methods including substantially closed-loop systems.